This is an application to investigate the mechanisms of microvesicle biogenesis in invasive tumor cells. It builds on exciting findings generated with previous NIH funding on a unique population of vesicles, called microvesicles that contain functionally active proteases and are released by tumor cells as they acquire invasive potential. The release of protease-loaded microvesicles may serve as a mechanism to bring about matrix degradation and perhaps even deposit paracrine information at distal locations, thus creating paths of least resistance as tumor cells invade and migrate through surrounding tissue. This is distinct from pericellular proteolysis at invadopodia, which enables localized matrix degradation juxtaposed to the leading edge. Discovering that there may exist more than one mode of proteolytic invasion, limits the effectiveness of any invasion-targeted therapeutic strategy that does not include both focal and distal proteolysis. While a significant amount of research has been directed to the understanding mechanisms of invadopodia formation and function at sites of cell invasion, microvesicles biogenesis and function remains a relatively understudied area of tumor biology. However, recent accruing evidence demonstrating the bona fide presence of microvesicles in body fluids (blood, urine and ascites), and their potential to serve as indicators of disease, has extended interest and intensified research efforts in microvesicle biology and function. The overarching objective of this application is to define molecular mechanisms of microvesicle formation. The project focuses on the central hypothesis that specific ARF and Rab proteins direct membrane type proteases and other proteins to sites of microvesicle biogenesis and that tight interchanges between RhoA and Rac1 signaling governs the plasticity required for switching between microvesicle and invadopodia-mediated proteolytic invasion. We will address two specific aims. In the first aim, we will define endocytic recycling pathways that direct cargo to sites of microvesicle biogenesis as well as examine how recruitment of specific Rab effectors regulate actomyosin-based contraction required for microvesicle biogenesis. In the second aim, we will examine the spatial activation of RhoA and Rac1 in invasive tumor cells. We will also investigate potential mechanisms that regulate Rac1 down regulation during microvesicle formation and how Rho signaling facilitates the process. Given recent heightened interest in the biology and clinical promise of microvesicles, these investigations are highly current. They will advance present understanding of microvesicle biogenesis and have potential to provide targets for diagnostic as well as therapeutic application.